The warrior cats use lots of words and phrases that we don't, and if you have any problem understanding what a cat has said, here is a quick glossary you can use, sorted conveniently in alphabetical order.
Crowfood - Old, rotting prey.
Fresh-kill - Prey that has been caught that day
Foxlength - About a yard
Gathering - A meeting among cats from all Clans that happens once a month, where the leaders share their Clan news
Greenleaf - Summer
Halfbridge - A human dock
Horseplace - A horse ranch
Kittenstep - About a centimeter; an inch or less
Leafbare - Winter
Leaf-fall - Fall or autumn
Monster - A human vehicle, usually a car
Moon - A full month; the time it takes for the moon to complete its cycle
Moonhigh - When the moon is at its height; around midnight
Moonpool - A place in the new lake forest where Clan cats meet to speak with StarClan
Moonstone - A place in the old forest where Clan cats met to speak with StarClan
Mouselength - About the length of a mouse; an inch or two
Newleaf - Spring
Quartermoon - A week
Rabbitlength -About a foot
Silverpelt - A belt of stars in the sky; each star represents a StarClan cat
Sunhigh - When the sun is at its highest; around noon
Taillength - About a foot
Thunderpath - A road, usually a highway
Twoleg nest - A human house
Twolegplace - A string of human houses; a human town