Credit utilisation
How much of your available credit you are currently using, expressed as a percentage.
If you have 10,000 of available credit across your cards and are using 3,000, your utilisation is 30%.
In countries that use credit scoring, lower generally reads better to lenders. Which produces the counterintuitive result that closing a paid-off card can make your position look slightly worse, because it removes available credit while leaving your balances unchanged.
How much this matters varies enormously between countries — some systems weigh it heavily, others barely track it. Treat the principle as directional and check the specifics where you live before acting on it.
It is also secondary to the actual question, which is whether an open card is a temptation you would be better without.
Related terms
Covered properly in Learn.