Meaning of -fold

Question

I saw this text while reading wikipedia(http://en.wikipedia.org/wiki/K-means%2B%2B)

The authors tested their method with real and synthetic datasets and obtained typically 2-fold improvements in speed, and for certain datasets close to 1000-fold improvements in error.

and I'm curious about the meaning of -fold, like 1000-fold, 2-fold. Is this a kind of unit? or something? Can anyone give me some references about this term?

Answer 1

Twice as large/great/many/etc. A clear method of saying 'I increased the speed by two fold' would be 'I doubled the speed'

Answer 2

It's essentially a multiplier. Read it as 2 times.

Answer 3

It just means "multiple" - so 2-fold is twice as fast and 1000-fold is 1000 times as fast...