Team is a very interesting concept. At a very basic level, a team is a group of people put together to achieve a special objective. But, a well-formed team is way more than a group of people. Its output could be way more than sum of the outputs of the individuals comprising the team. A great team could help the individuals achieve way more than they individually can.
For examples of what a team is, think about a sports team - let's say Golden Gate Warriors from NBA, the Manchester United from Soccer; or think about a group of people that did something amazing in a movie - the team that did the job in the movie the Italian Job, or how about Ocean's Eleven, even James Bond has a small team.
In your technology or software or information technology projects, you will one or more teams working. The individuals in the team are called team-members.