operators - What does the percent sign mean in PHP?

What exactly does this mean?

$number = ( 3 - 2 + 7 ) % 7;

Answer

It's the modulus operator, as mentioned, which returns the remainder of a division operation.

Examples: 3%5 returns 3, as 3 divided by 5 is 0 with a remainder of 3.

5 % 10 returns 5, for the same reason, 10 goes into 5 zero times with a remainder of 5.

10 % 5 returns 0, as 10 divided by 5 goes exactly 2 times with no remainder.

In the example you posted, (3 - 2 + 7) works out to 8, giving you 8 % 7, so $number will be 1, which is the remainder of 8/7.