thousands of
fixed phr..fixed phr.. A very large number of people or things. You use it to talk about a big amount without giving an exact number.
fixed phr.. A quantifying phrase indicating a large, indefinite number, typically in the low thousands. It functions as a predeterminer before a plural noun.
Thousands of birds fly south for winter.
Thousands of fans gathered outside the stadium, hoping to get a glimpse of the team.
The archive contains thousands of uncatalogued manuscripts, representing a monumental task for future historians.
Always followed by a plural noun, like 'thousands of people' or 'thousands of years'.
Contrast with 'a thousand' (exactly 1,000) and 'hundreds of' (a smaller large number); 'thousands of' emphasizes a large, impressive quantity.
I saw thousand of birds.I saw thousands of birds.The word 'thousand' must be plural ('thousands') when it's used with 'of' to mean 'a lot'.