This is the 2116th most frequent Chinese word.
塞
"塞" means "to fill," "to stuff," "to block," or "a fortress."
塞 is used as a verb meaning 'to stuff or insert something into a space.'
我把书塞进背包里。
I stuffed the book into the backpack.
塞 is used as a verb meaning 'fit or squeeze something into a space.'
这个瓶口太小了,不能塞入果冻。
This bottle's opening is too small to fit the jelly in.
塞 is used as a noun meaning 'blockage or congestion,' specifically relating to traffic jams in this case.