grammatical number - When to use word "experience" in a singular form and when in plural?

I always thought that the word experience is only singular, but I see people using it as a plural.

Does word experience has plural form and in which cases it is proper to use it?

Answer

It depends on what meaning of experience you are using, as some meanings are countable nouns while others are uncountable. It's not clear which meaning you are asking about in your question, but we can look at the two major meanings.

If you are talking about how much experience you have (e.g. work experience), it is an uncountable noun and it does not have a plural form. You can't say

* I have a lot of experiences as an accountant.

… if what you mean to say is that you have worked as an accountant for a long time. This meaning of experience is uncountable, so you instead would say

I have a lot of experience as an accountant.

(This usage is similar to the usual meaning of the word money: “You have a lot of money”, “I have no money.”)

By contrast, if you are talking about experience meaning an event, such as travelling to a particular place on a particular date, or being present for a memorable happening, then it can be plural to indicate multiple such events:

I have had many interesting experiences while travelling abroad.

In this meaning, it must be plural if there are multiple events; you cannot say:

* I have had many interesting experience while travelling abroad.

And of course, if there is only a single event, you can say:

I had only one interesting experience while travelling abroad.