Context: In some team matches, only one entrant from each team may be designated as the "legal" or "active" wrestler at any given moment. Two wrestlers must make physical contact (typically palm-to-palm) in order to transfer this legal status. This is known as a "tag", with the participants "tagging out" and "tagging in". Typically the wrestler who is tagging out has a 5-second count to leave the ring, whereas the one tagging in can enter the ring at any time, resulting in heels legally double-teaming a face.

Question: What does a "tag" entail?
Answer: Two wrestlers must make physical contact (typically palm-to-palm) in order to transfer this legal status.

Question: What are two things that can be done with tagging?
Answer: "tagging out" and "tagging in".

Question: How long does a wrestler have to leave the ring once they are tagged out?
Answer: has a 5-second count to leave the ring

Question: How much time does a wrestler have once they tag in? 
Answer: the one tagging in can enter the ring at any time, resulting in heels legally double-teaming a face.