Sexual assault occurs when someone touches someone else in a sexual manner without their consent. It is also known as rape though the term "sexual assault" is generally considered broader (encompassing some acts which some people do not consider to be rape). Sexual assault is illegal in most jurisdictions. However, many sexual assaults are not reported or prosecuted, because of attitudes which tend to minimise the seriousness of the act or tend to blame women (and other victims) for their own assault.
Sexual assault in general
One of the primary English-language resources for information about sexual assault is RAINN, the Rape, Abuse, and Incest National Network. Their information page provides general information and statistics about rape in the United States.
Some basic stats:
- As many as 1 in 4 women have been sexually assaulted
- Most people are sexually assaulted by someone they already know (not a stranger)
- 60% of sexual assaults are never reported
It is important to remember that people of any gender can be the victim of sexual assault. However, women are the vast majority of sexual assault victims, and the fact that people of other genders are sometimes sexually assaulted should not be used as a derailing tactic in discussions about sexual assault.
Here are a couple of definitions of sexual assault:
- "Any involuntary sexual act in which a person is threatened, coerced, or forced to engage against their will, or any sexual touching of a person who has not consented." -- Wikipedia
- "Sexual activity to which a person does not consent" -- Royal Women's Hospital 
- "The term "sexual assault" covers behavior from unwanted touching to rape." -- Northwestern University Women's Center
- "Sexual assault is any type of sexual contact or behavior that occurs without the explicit consent of the recipient. Falling under the definition of sexual assault are sexual activities as forced sexual intercourse, forcible sodomy, child molestation, incest, fondling, and attempted rape." -- US Department of Justice
- "Rape is forced sexual intercourse, including vaginal, anal, or oral penetration. Penetration may be by a body part or an object. Sexual assault is unwanted sexual contact that stops short of rape or attempted rape. This includes sexual touching and fondling. (But, be aware: Some states use this term interchangeably with rape.)" -- RAINN 
It's important to note that most reputable sources (including research institutes, legal/justice resources, and other organisations that deal with the issue as a major part of their job), and even disreputable sources such as Wikipedia, define sexual assault as including any form of sexual contact without consent, including groping, fondling, and the like.
In online discussions, apologists sometimes say that an incident "wasn't really sexual assault" in an attempt to minimise or dismiss the seriousness of it. Feel free to point them here.
Sexual assault in geek communities
Sexual assault is present in the geek community, as in any other community.
- Geek events such as technical conferences and science fiction conventions provide an environment in which sexual assault can easily occur
- Few geek events have policies for dealing with sexual assault or harassment which occurs at the event
- Geek Social Fallacies may cause geeks to be unwilling to ostracise anyone, even a rapist
- Double standards and rape culture mean women are encouraged to dress sexily or cosplay at geek events, then told they were "asking for it" if sexually assaulted
- Many geeks use the word "rape" as a joke or in a way that minimises and normalises it (e.g. gamers using it as shorthand for "handily defeating another player")
- Some communities (especially gamers) intentionally use threats of sexual violence to intentionally terrorize and exclude women
There are numerous first-hand accounts of sexual assault at geek events. The Geek Feminism blog has gathered some of them under Worst con experiences. See below, under "Incidents", for other examples.
- Noirin Shirley ApacheCon incident
- Sexual assault at Southeast LinuxFest
- Julian Assange arrest for sexual assault
- Codemash sexual assault
- CONFidence 2013 assault
- Groping at FOO Camp
- F.I.R.S.T. Robotics groping incident
- Harlan Ellison groping Connie Willis
(Also search within Timeline of incidents for the term "assault", "groping" and similar, as some incidents do not have pages of their own.)
Combatting sexual assault in geek communities
- Geek events should have a Conference anti-harassment policy which clearly states that harassment (and sexual assault) are not permitted, and providing procedures for dealing with incidents
- Note that not all incidents should necessarily be reported to the police, nor should a victim be pressured into doing so if s/he doesn't want to. Consider, for example, a man who is going around the conference groping women's breasts without their consent. He should be asked to leave the event even though his behaviour may not be legally actionable in many jurisdictions.
- As an individual, be a good ally
- Educate yourself about sexual assault
- Never blame the victim!
- Know where to refer someone if they need help (eg. a rape crisis hotline in your local area, or conference directors in charge of security and policy enforcement at geek events)
- Read this: What to do when someone approaches to tell you about sexual assault or abuse
- Fight rape culture. If you see someone joking about, minimising, or advocating rape, tell them it's not okay. Sadly, this works best when coming from men to men -- women's complaints are often ignored.
- Don't fall victim to the Geek Social Fallacy that "ostracisers are evil". Toxic people -- including sexual predators and those who harass and sexually assault members of our community -- need to be ostracised.
On reporting sexual assault to the police:
On fighting back:
- Why don't you just hit him? (Geek Feminism blog)
- Why didn't you just kick him in the balls? (rachelmanija on Dreamwidth)
- Disturbing the universe is a social gaffe (oursin on Dreamwidth)