A majority lynch is a voting ruleset which means, in order for a lynch to occur, a single player must have more than 50% of the votes in order to be lynched. This means that no one else could possibly have more votes, or an equal number of votes, to the player who is being lynched. In most cases, if a majority is not reached by the end of a day deadline, the day will end in a no lynch.
Usually, once a player has reached a majority, votes can no longer be changed.
This is the most common method of resolving a lynch and is the only one that is considered normal.
If there are 13 players alive, any single player must have 7 votes to be lynched (54%).
If there are 12 players alive, any single player must still have 7 votes to be lynched (58%) as 6 votes is only 50% which is half and not a majority (it's exactly 50%, not more than 50%).
This means that it is harder to achieve a lynch with an even amount of players. It is very common for players to no lynch when there is an even amount of players for various reasons.