if the jump start gave it enough juice to start on the key, then is is
almost certainly the battery. Left the lights on?
Has it been a bit lazy on turn over?

If this is sudden, you may have an electrical fault which is draining the
battery - a faulty diode in the alternator maybe?

Charge the battery well (over night) and see if it holds charge (with a
meter) if it drops slowly, it sounds like the battery is life-expired - they
are typically only good for 5-8 years max (don't care how long all you lot
HAVE had a battery last before you start posting that your uncle's model T
is still on the original or whatever).

If the charge on the battery drops very quickly - you might have a fault on
the car itself - this is not common - my money is on a new battery.