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.
See: 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.