RUSHES

Tower rush - This is when towers are build with in a base.

How to - Get your villagers onto his land and build towers by wood, gold, stone, or town centers
Defense - Kill the peasents making the towers or build towers of your own to stop the peasents from moving further into your land.

Chariot Archer Rush - This is when he sends a group of chariot archers to kill your villagers.

How to - Make an archery range as one of your first buildings you make and crank out chariot archers then when you have 5-7, attack
Defense - This is a rush that can come early since you don't need gold to make chariot archers. Use a wall to defend and if he transports make sure you have a couple ballistas ready

Horse archer rush - This is when a group of horse archers is sent to kill your villagerss.

How to - Read chariot archer rush. Need gold for this one tho.
Defense - Similar to the chariot archer rush but will come later since horse archers require gold.

Cavalry rush - This is when a group of cavalry units is sent to destroy you.

How to - Make some stables, then make chariots at first, then as you mine more gold, make cavalry units, attack when you're ready. The more the better (but don't attack to late).
Defense - This can be hard. If 15 cavalry units come at you 5 min into the game....
you better have a nice wall, several towers, and a lot of ballistas

Seige rush - Seige weapons are sent to destroy you

How to - Make a seige workshop and get wood and gold to make seige weapons the faster you can get the resources and attack, the better the rush.
Defense - This is a kinda slow rush If you tower up your coast you shouldn't have a problem since they will probably be ballistas and stone throwers without a lot of techs. Just use cavalry or your own seige weapons to counter.

Barracks Rush - This is when your opponent builds a lot of barracks on you land and cranks out footsoldiers to attack your base.

How to - You have to get your villagers onto his land within the first minute.
Then find a location close to his base yet hidden. Build about 4 barracks and make swordsmen and attack.
Defense - A really tough rush. But it doesn't really work unless they get on your
land within the first minute of the game. So just make sure he doesn't
get on your land early in the game and it wont be a problem.

Elephant rush - When a couple elephants are sent early in the game (works best with a couple seige weapons)

How to - Make a stables. Make a couple of elephants and send them to attack (try to send maybe a priest and a couple seige too, It may take longer to make the units so if you can make them fast enough, do it)
Defense - Priests. If he has siege weapons you gotta destroy them first or he will
kill your priests with them.

These are the basic rushes. There are offshoot of these rushes like the jihad-seige tower rush
and the heavy cavalry rush.