Sinsemilla is a term describing the cannabis plants that are not pollinated hence lacking seeds, if a female cannabis plant is not fertilized it will contain seedless pods with large amounts of resin resulting in a more potent cannabis. A sinsemilla strain is produced by removing the male flowers from existence before they release pollen grains, enabling the plant to focus all the seed producing energy into bud producing energy.
Merriam-Webster Online Dictionary
sinsemilla (noun) highly potent marijuana from female plants that are specially tended and kept seedless by preventing pollination in order to induce a high resin content , also a female hemp plant grown to produce sinsemilla
seedless cannabis, unseeded marijuana, sensi, seed-free weed, high-potency cannabis