What is this wierd string format many plugins use?

I have seen many plugins that use a certain type of string format when they save the data in the database.

I dont know why they are not using JSON, but below is an example thats put in the wp_postmeta table in the meta_value column:

a:5:{s:5:”party”;i:5;s:5:”email”;s:20:”example@gmail.com”;s:5:”phone”;s:8:”12345678″;s:2:”ip”;s:12:”86.52.104.45″;s:15:”date_submission”;i:1595861062;}

This were made by the “FiveStarPlugins Restaurant Table Reservation”.

When i book a table, they put some data as my email, phonenumber etc in there.

What kind of format is this?
Why is it not JSON?
And how do i decode it?

Thanks in advance