In case you didn't get a chance to look them up, the short answers:
These are all metrics 4 are used to calculate routes, the other 2 (you are missing hop count) are used in other ways. These are IGRP Metrics (I assume).
1) Load - How heavily utilized is the given link (the link could be faster that another link, but if it is overloaded with traffic - a slightly slower link may be a better choice. Faster is not always better).
2) Reliability - what is the error rate of the link ( Ratio of packets that arrive undamaged).
3) Max Transmission Unit (MTU) - The maximum size of a packet (datagram), this is not for calculating routes - just tells other routers what size packet it can accommodate. If the packets are larger than the MTU, they can be broken up into 2 or more packets.
4) Bandwidth - speed of the link (1200 bps - 10 Gpbs, defaulting to T1 speed of 1.544 Mbps).
5) Delay - measures the amount time to traverse the link in the network. The sum of the delays of other routers it must go through in a route.
6) Hop count - ( the one not mentioned and is not used by IGRP to calculate route - just to prevent routing loops). Hop count is maintained by IGRP as a threshold comparison. If you have passed the number of hops defined (up to 255), routes are invalidated.