When we post a comment, we send it to an online website.

We can post a letter, which means that we send a letter to someone.

 

A mouse is a small grey animal.

A mouse is a device that we use when we use a computer.

 

A link is a connection between things.

A link may be also an URL address of the website.

 

Mobile means that something can be moved from one place to another.

Mobile also relates to wireless devices such as phones.