The term UART (Universal Asynchronous Receiver Transmitter) is the technical term for the good old serial port found on most MCUs. The term USART similarly refers to a serial port capable of handling both synchronous and asynchronous operation. Over the past few years, Microchip has been integrating an updated serial port into many of their MCUs known as the Enhanced Universal Synchronous Asynchronous Receiver Transmitter or EUSART.
The main feature of EUSART is the ability to auto-detect the baud rate of received signals. An example of of a chip featuring EUSART is the PIC16F688, which is the subject of a Microchip App Note covering the use of EUSART.
A practical illustration of the EUSART in action is this sample project from ENMCU using the PIC18F2455 to detect the baud rate of a serial character received and display the speed on an attached LCD.