strpos()
you can use this function to find a word or letter or number in a string, it its found, it will retrun true.
more info at
http://php.net/manual/en/function.strstr.php
example, lets say i want to know if $string has any words wallpaperama in it
$string = 'wallpaperama has cool and amazing wallpapers';
$find = 'wallpaperama';
if(strpos($string, $find ){
echo 'yes, its found'
}else{
echo 'not found';
}
echo 'yes, its found'
}else{
echo 'not found';
}