If an Apple means an apple to everyone, same for an orange then why definition of feminism is different for everyone.

An apple is something that can be seen. We all know what an apple looks like, so it's meaning is pretty much universal.

Feminism is a more abstract concept. We all come to know about it in different ways and have different experiences with it, and thusly have our own opinions (influenced by our general life experience, naturally) about it, which results in there being various definitions of it.

well theres different kinds of apples right?

not all apples and oranges are the same.:)

Because it's a movement with no defined leader, not just one belief.

One is abstract, one is concrete.

One is tangible. They know what it is as an absolute. But even with the fruit what is intangible like the taste is perceived slightly different by everyone.
One is perception. Their own personal judgment derived from experience or observations colours their thinking.

There are different kinds of apples and they all vary greatly in flavor.