Users without full edit privileges can suggest edits to posts and tag wikis.
Users with 2,000 reputation have the ability to edit any question or answer. This is called "edit privileges".
Users (both registered and cookie users) who have not reached the level of 2000 reputation (or 100, for community-wiki posts) are allowed to suggest edits. These are not applied immediately, but go into a queue where users who have edit privileges can vote to approve or reject them.
If your edit gets approved, you get 2 rep.
If your edit is rejected, a reason will be displayed on the suggested edit page. You can track your suggested edits under the suggestions section of the Activity tab on your account profile.
The suggested edits feature also applies to users who don't have 20,000 reputation to suggest edits to tag wikis.