A lot of instructors/teachers/educators say and claim that Wikipedia is a bad source for facts, and you should not use it. Yes, this is correct.
Anything on Wikipedia can be changed by literally anyone. Even without approval. This leads to people changing articles to include false facts about things, and making things opinion based, rather than true facts. This also leads to people learning false facts.
A simple alternative to Wikipedia, is dictionary.com. Dictionary.com can provide millions of definitions for millions of words. The difference is, the public cannot edit definitions. All definitions are facts, and cannot be modified by anyone besides the people who manage dictionary.com.
Another issue with Wikipedia is privacy. When you make a modification to an article or definition on Wikipedia, unless you are logged into a Wikipedia account (most people aren't), your IP Address is public and now visible to everyone, on the Wikipedia article you edited. All someone needs to do is go to the edits tab, see you edited the article, and your IP Address is right there, public on Wikipedia, visible to anyone in the Universe. Usually, most people don't want random people looking at their IP Address, having the ability to do ANYTHING to it, potentially finding where you live. VPN's are banned on Wikipedia, so there is no getting around this.
Even if Wikipedia was a reliable source, you should never base your facts off of a single source, and you should check with multiple sources first to see if the facts all match up. The same goes with dictionary.com, and any other Encyclopedia/dictionary.