Donald Trump now has 1238 delegates supporting him at the Convention, one more than the 1237 needed for an absolute majority.
Although Trump was not expected to reach this number until June 7 when the next Republican primary elections are held, he was able to get over the top a little early. Trump still does not have enough pledged delegates for a majority, but several States are sending unpledged delegates. Trump was able to get enough of those unpledged delegates to announce publicly that they would vote for Trump at the Convention to put him over the top.
Theoretically, these delegates are not bound by their promise and could change their minds at any time. The reality though is that Trump will receive enough pledged delegates on June 7 when California, New Jersey, and a few other States hold their primary elections. Getting these delegates to announce early just created a media story a few weeks early that continues the message that Trump is the winner.