Rules and Guidelines For Steam: Discussions, Reviews, and User Generated Content
These guidelines apply to all places in the Steam Store and Community where users can post content. This includes, but is not limited to, discussions, comments, guides, product reviews, screenshots, artwork, videos, tags, Steam Workshop, and Steam Greenlight.

When providing feedback, posting information, or discussing a product in Steam, whether it’s negative or positive, please make sure you are being relevant, constructive and polite. Developers take feedback from all kinds of sources into account, even though they may not have the time to respond to every post or question.

Please note that Administrators/Moderators reserve the right to change/edit/delete/move/merge any content at any time if they feel it is inappropriate, abusive, or incorrectly categorized.

All users are subject to the Steam Subscriber Agreement and Steam Online Conduct.

General Rules
Do not do any of the following:

Flame or insult other members
Bypass any filters
Abuse or encourage abuse of the Post Reporting System
Post personally identifiable information (i.e. name, address, email, phone number, etc.)
Bump threads
Derail a thread's topic
Post links to phishing sites
Post spam (i.e. +1, 10char, rickrolls) or Re-post Closed, Modified, Deleted Content
Repetitively post in the incorrect forum (example: trade requests belong in trading forum)
Openly argue with a moderator
Artificially manipulate the User Review system or voting/rating systems
Content Rules
Do not post any content on Steam containing the following:

Porn, inappropriate or offensive content, warez or leaked content or anything else not safe for work
Any discussion of piracy will result in a permanent ban from the Steam Community including, but not limited to:
Cracks
Key generators
Console emulators
Cheating, hacking, game exploits
Threats of violence or harassment, even as a joke
Posted copyright material such as magazine scans
Soliciting, begging, auctioning, raffling, selling, advertising, referrals
Racism, discrimination
Abusive language, including swearing
Drugs and alcohol
Religious, political, and other “prone to huge arguments” threads
No Backseat Moderating
Let the moderators do the moderating. Backseat moderating is when people who are not moderators try to enforce the forum rules. If you see a person breaking the rules, take advantage of the Report () button or simply ignore the offensive post(s), thread, or review.

Report Posts to Moderators
Should you observe a fellow Community member breaking these rules please report the post or item by clicking the Report () button located on every item, post, and review.

Repeated Offenders
Repeated offenders of the above rules and guidelines will be banned from the Steam Community. Any moderator has the ability to ban a user for violating the rules at their discretion.

source : https://support.steampowered.com/kb_article.php?ref=4045-USHJ-3810