user105424: When bitcoin transactions are made, I know that they are put into the mempool. After certain transactions are added to a block and that block gets verified, what happens to all the other transactions that did not meet that threshold? Do they just get rejected?

user38618: Addition to darosior's answer:
Remember that there's no single mempool - every node maintains its own. Thus a miner can mine a transaction after a long time if it's still valid (its input not spent by another transaction.)

user101498: 
Do they just get rejected?

No, they will just wait for another block to be included in.
Note that transactions have a time to live in the mempool of 336 hours (configurable using the maxmempoolexpiry startup option). 

105424: <p>When bitcoin transactions are made, I know that they are put into the mempool. After certain transactions are added to a block and that block gets verified, what happens to all the other transactions that did not meet that threshold? Do they just get rejected?</p>
 38618: <p>Addition to darosior's answer:</p>

<p>Remember that there's no single mempool - every node maintains its own. Thus a miner can mine a transaction after a long time if it's still valid (its input not spent by another transaction.)</p>
 101498: <blockquote>
  <p>Do they just get rejected?</p>
</blockquote>

<p>No, they will just wait for another block to be included in.</p>

<p>Note that transactions have a time to live in the mempool of 336 hours (configurable using the <code>maxmempoolexpiry</code> startup option). </p>
