skip current iteration

You are looking for the continue statement. Also useful is break which will exit the loop completely. Both statements work with all variations of loop, ie. for, foreach and while.

$numbers = array( 1, 2, 3, 4, 5, 6, 7, 8, 9 );
foreach( $numbers as $number ) {
    if ( $number == 4 ) { continue; }
    // ... snip
}