To "split" something means to share it equally between people. It's often used in a restaurant setting. Things that people often "split" include:

• split an appetizer (at a restaurant)
• split a dessert
• split the check

You can split something with another person:

Do you want to split this with me?

Or you can split something between a group of people:

We'll just order a few salads and split them between us.