WHAT IS 420?

i dont know 420.. what is 420??

tell me pls !...

generally 420 is a number which represent to a fraudulent activity done by anyone. Like if any one making fools to people and getting money them then we can call him/her a 420 person.

It depends...4:20 is the time to smoke weed.

Look at here https://it.wikipedia.org/wiki/420_(cannabis)

It's the signifies for smoking weed all freaking day and enjoy it. XD
On a serious note, if you don't mean pot, then I don't know the technical of it.