What is Casual Games?

I have so much confused that what is the casual games. When I saw it on amazon I don't know what that.

but the Google can help me in this issue when I search. I found that it is a Puzzle games,action arcade and card board and some a little game.  likes Mahjong,Brick buster

Wow that all my favorite game, All that easy game that used for relax in space times some of that we can play on smart phone.

for me only don't know about the vocabulary, Casual.

Ok Do you like some Casual Games that I offer to you?

Big Kahuna Reef [Download] $0.00	100% Hidden Objects [Download] $6.99	Ticket to Ride [Download] $9.99
The Otherside: Realm of Eons [Download] $2.00	Drip Drip [Download] $9.99	Plants vs. Zombies [Download] $9.99