It is a word used in Chile that replaces the word "thing", so it can be used replacing every single noun that exists. It doesn't mean anything wrong but is not a nice way to talk. It is mostly used with people that have the same status or relation.
The actual meaning of the word wea depends of the context of the situation.
"Pásame esa wea" (give me that thing)
NOTE: In this situation, when saying "wea" the person should indicate the thing that she or he refers to.