The previous two people are correct. It is also known as Gen1. It is the size of a tama mini. It has no connection but is fun, I've tried the next version after (P2 or Gen2) which is the exact same thing except the characters are slightly different.
A P1 is the first Tamagotchi that was released in 1996. It has only one game and is not able to connect. It doesn't have a lot of characters but it has some bas ones. It is slightly bigger than a Chibi Tamagotchi. It is quite simple. It is Generation 1 of Tamagotchi. But it is known as P1. I hope I clarified something here for you.