ladder

(noun) steps consisting of two parallel members connected by rungs; for climbing up or down.

(noun) ascending stages by which somebody or something can progress. Examples: "He climbed the career ladder."

(noun) a row of unravelled stitches. Synonyms: run, ravel. Examples: "She got a run in her stocking."

(verb) come unraveled or undone as if by snagging. Synonyms: run. Examples: "Her nylons were running."