PPTP stands for Point-to-Point Tunneling Protocol. PPTP, operating on TCP port 1723, is one of the oldest VPN protocols still in use, having been around since Windows 95 and standard on all versions of Windows since. PPTP was developed by a Microsoft initiative to encapsulate another protocol called PPP (Point-to-Point Protocol).
Out of all the VPN protocols, PPTP is one of the most common, easiest to set up, and computationally fastest. For that reason, PPTP is useful for applications in which speed is paramount, like audio or video streaming, and on older, slower devices with more limited processors.
However, PPTP is also subject to serious security vulnerabilities. Its underlying authentication protocols, usually MS-CHAP-v1/v2, are fundamentally unsecure and have been repeatedly cracked in security analyses since PPTP was introduced.
For this reason, PPTP is NOT recommended except in cases where security is absolutely non-essential. PPTP is now only available on ExpressVPN through manual configuration. You can find PPTP manual configuration guides for Windows 10, Linux, iOS, and routers.