full of people or things that are pushed closely together: jam-packed with The streets were jam-packed with tourists.

to allow something new to start

to prevent something happening smoothly in the way that it was planned, by causing a problem or difficulty.

at the most modern stage of development in a particular type of work or activity

a small or insignificant member of a larger organization or system.

the detailed or complicated facts of something

someone or something that functions very well or efficiently

something that is very old-fashioned and should no longer be used

If you talk about the nuts and bolts of a subject or an activity, you are referring to the detailed practical aspects of it rather than abstract ideas about it.

To revise something (such as a plan) from the beginning, typically after it has failed / start over

very advanced in its development

a sudden success that lasts only a short time and is not likely to be repeated