In the context of radio frequency / spectrum, a block is a subset range of radio frequencies within a larger band.
For example, in the US, the whole PCS band spans 1850 - 1995 MHz. This is sub-divided into seven blocks, each spanning a specific 10-30 MHz-wide portion of the band. In any given geographic area, different companies own licenses for different blocks within that band.
When governments auction off radio frequency bands to, they usually offer many licenses that can be bought by different companies. Bands are usually divided into licenses two ways: by blocks and by geography. Therefore one license sold at auction will cover only one block (not the whole band) and only one geographic area of the country.