Basis point
One hundredth of a percentage point, so 100 of them make 1 percent. The unit exists so that a change in a rate cannot be read in two different ways.
A basis point is one hundredth of a percentage point. 100 basis points make 1 percent, 25 basis points make a quarter of a percent, and 1 basis point is 0.01 percent. It is written bp or bps and said out loud as bips.
It exists to remove an ambiguity that costs real money. A nominal rate of 4 percent that rises by 1 percent could mean 5 percent, a rise of one percentage point, or it could mean 4.04 percent, a rise of one hundredth of its own size. A rise of 100 basis points can only mean the first. Central bank decisions, bond yields and fund charges are all quoted this way for exactly that reason.
The unit is also where small numbers do their quietest damage. An annual fee of 50 basis points is half a percent, and half a percent taken every year compounds against you in the same way returns compound for you: over 30 years at a 7 percent gross return, it takes roughly 13 percent of the final balance. The compound interest calculator runs the same mechanism in the direction you want it to go.
The one habit worth keeping is never mixing units inside a calculation. Convert basis points to a decimal before anything else, so 75 basis points becomes 0.0075, and an annualised return quoted in percent never gets a figure in basis points added to it.