Jam (up) is a term used to describe a situation where something is stuck or blocked. The crossword solutions for this term are GUM (3 letters), CLOG (4 letters), and OBSTRUCTION (11 letters). GUM is a sticky substance that can be used to stick things together, while CLOG is an object that can block a pipe or other opening. Finally, OBSTRUCTION is an act of blocking or hindering something from progressing. All three of these terms can be used to describe a jam (up) situation.