Crawling is making repeated plays on the second line.
Here it is Black who is crawling in response to White's attacking plays and . This is a very poor position to be in. Even if Black survives here, the territory gained will be small in relation to the influence of White's wall.
It is for this reason that there is a proverb: the second line is the route to defeat. Crawling plays are sometimes a necessary evil (see to crawl or not to crawl; but before the endgame they are most often essentially loss-making.