It is uncountable, it may mean many things but in practice it is generally used as though it is singular. Hope this helps :)

Singular. Words like this are known as "collective nouns". Such words are singular but describe a collection of things. Other examples of collective nouns are: flock, populace, collection, army, jury, family, tribe, gang, cutlery There are a few words that are both singular and plural, though they may have different meanings when used as singular or plural. Look up "people" as a good example of this.

It's an uncountable noun so it's only used in singular. I have so many things in my bag. I have so much stuff in my bag.