Breakout cables (harness/fanout) have an MPO connector at one end and a corresponding number of duplex LC connectors at the other end (4, 6, 8 or 12), other connectors are used, but LC is by far the most popular option.
In a Data Centre environment with ever-increasing bandwidth and network connections, conventional duplex fibre leads are unable to meet these increased demands. This is where MPO cables are the perfect solution. A single MPO connector can house up to 24 fibres in a form-factor that is very similar in size to a duplex LC connector. Using MPO trunk and breakout cables allows much higher density cabling.