What is modem asynchronous data?

In asynchronous serial communication at the physical protocol layer, the data blocks are code words of a certain word length, for example octets (bytes) or ASCII characters, delimited by start bits and stop bits. A variable length space can be inserted between the code words. No bit synchronisation signal is required. This is sometimes called character oriented communication. Examples are the RS232C serial standard, and MNP2 and V.2 modems and older.