The target in relation to bitcoin mining is generated by the network. The miners job is to find a hash below the target hash, not one specific hash. This is because the hashing algorithm has so many potential inputs (see high-min entropy) that it would be impossible for miners to calculate one specific hash. Once miners find a hash below the target hash they have found the target and are rewarded.

Lets look at a simple example. Say we had the numbers 1-100 and hashed the output. If the hash target was 75, then in Bitcoins case the target would be anything below 75. So when guessing the input we would have a 75% chance out of 100 to guess correctly. This is very easy to achieve. So if we wanted to make it harder, we would reduce the target to 5 (and the bitcoin network would do this automatically). That way miners would have a 5% chance of guessing correctly, taking them a longer time.

If we take this analogy and multiply it by a much larger data set, we would have the basic idea of the Bitcoin mining target and how it readjusts to meet the 10 minute rule.