Can someone explain "procs" to me?

[sarahe484]

I was asking my guildmates why kraken gear costs tens of millions of dollars, when I've spend less than 1M gold on each of my gear/weapon items and my stats are better. They said it's all about the procs. But I have no clue what procs are or how to see which weapons/gear have good procs.

Can someone explain procs to me like I'm a five year old?