(obsolete) Rich in herds (of cattle etc.).

The amount that constitutes a herd.

(sports) A non-official path created by hikers, and usually maintained by the hikers themselves.

(epidemiology) The indirect protection against the spread of a contagious disease in a given population caused by the immunity of a significant proportion of the population to that particular disease; the immunity may have been obtained through having survived the infection or through vaccination.

(Internet, computer security) A large collection of compromised systems exploited for malicious purposes.

(idiomatic, in similes) To attempt to control the uncontrollable. / Used other than figuratively or idiomatically: see herd, cat.

(sociology) herding instinct.

(sociology) the tendency of a group of individuals (a herd) to react coherently without there being any coordination between them. The term may be applied to animals, or to human phenomena such as stock market bubbles and behaviour in political demonstrations.

(transitive, idiomatic, US) To supervise a group of people and their work.

A stud boar, a male pig kept for breeding.