"Touch base" is correctly spelled as two separate words: "touch base." It is a common expression used in informal communication to indicate the need for a brief conversation or update.

You can touch the base with the ball if you want to. Any part of the fielder's body can touch a base as long as he has possession of the ball.

To "touch base" means to briefly contact an acquaintance to get an update on what they are doing.

The saying 'let's touch base', comes from baseball. In baseball touching base is an important part of the game. When one says let's touch base, they want to share important information.

It is "touch".