A Private Pilot's License (PPL) allows individuals to fly aircraft for pleasure or personal travel, but not for pay. It is often the first pilot's license that someone earns and is usually required for more advanced licenses.
A Private Pilot's License (PPL) allows an individual to act as 'pilot in command' of an aircraft for private purposes, i.e. not for pay (more precisely, not for compensation). A PPL holder may carry passengers.
A PPL is often the first pilot's license that someone earns and it is usually a pre-requisite for more advanced licenses such as commercial or ATP licenses. The requirements for a PPL as well as the specific privileges it allows are different in different countries, e.g. a US PPL allows pilots to fly at night but a European PPL does not. PPLs are typically issued for a specific category or class of aircraft, e.g. someone may hold a helicopter PPL but not a fixed-wing PPL.
In some countries there may be other types of private license that are similar to a PPL but have different restrictions and privileges. For example, the US issues recreational and sport pilot certificates that are more restricted than a 'full' PPL.
Note that "license" is not always the correct term: in the US, the FAA issues certificates, not licenses, although informally many people refer to licenses anyway, probably because of an implicit comparison to a driver's license.