Single mode and multimode are each a type of fiber optic cable used to transmit voice or data between devices.
A single mode core is the smaller of the two cables and is able to carry light directly from one end to the other making it best for long distance applications. Single mode can achieve faster transmission rates because it is a single strand of data. Applications utilizing single mode will typically encounter less data loss and interference. However, single mode fiber is costlier and data transmission may be limited because of the size of the cable.
Multimode is best used for applications that run over short distances, or a local area network, and require the transmission of large data. Length is also dependent on the application and speeds required. 2km is considered the max distance before distortion becomes a problem. Over 2km dispersion occurs meaning the signals reach the destination at different times, thus making the data unreadable.
Single mode can convert to multimode, and vice versa, however a mode converter must be placed between the two lines to prevent data loss or disturbance.