a supply of something kept to be used if it is needed:
supply[countable usually plural]
$10 million in cash reserves
Somehow Debbie maintained an inner reserve of strength.
a quality in someone's character that makes them not like expressing their emotions or talking about their problems [↪ shyness]:
She overcame her own natural reserve.
an extra player who plays in a team if one of the other players is injured or ill [↪ substitute]
a team that plays when the usual team cannot do so
an extra military force that a country has in addition to its usual army, navy etc which can be used if needed [↪ reservist]
militaryalso the reservesPM
an area of land where wild animals and plants are protected [= reservation AmE, preserve AmE] ➔ nature reserve
for animals/plants[countable] British English
for native americans[countable]
a price below which something will not be sold, especially in an auction