The 25th amendment usually gets brought up when people are talking about presidential succession. Adopted after the assassination of JFK, the 25th amendment mainly lays out the path of power if a president is unable to do their job. The vice president would take the job next, as many already know. The 25th amendment has other sections as well, such as allowing the president to give up his power for an allotted time period to the vice president. This has occurred in cases where a president has a medical procedure to attend, for example, in which he may be unconscious. 

However, the central section of the 25A that has come up in the media recently is a portion where the VP can submit in writing to Congress that the president is not fit to serve. The president can then write back to defend themself. It would then be turned over to a vote in congress. If the VP wins the vote, the president must leave office, but if the president wins the vote, things return to normal (although we're sure that VP would lose his job). Essentially, it's another form of trying to get Trump out of office ASAP.

As reported by CNN, sources close to the situation say that Vice President Mike Pence has not ruled out using the 25th amendment against Donald Trump. However, Pence is being very careful not to do anything that may trigger Trump to do something insane before he leaves. If that is the case, 25A must be the last option because that would definitely send Trump into a rage