'Scrub oak' definitions:

Definition of 'scrub oak'

noun

Any of various chiefly American small shrubby oaks often a dominant form on thin dry soils sometimes forming dense thickets

From: GCIDE

Scrub \Scrub\ (skr[u^]b), n.
1. One who labors hard and lives meanly; a mean fellow. "A sorry scrub." --Bunyan. [1913 Webster]
We should go there in as proper a manner as possible; nor altogether like the scrubs about us. --Goldsmith. [1913 Webster]
2. Something small and mean. [1913 Webster]
3. A worn-out brush. --Ainsworth. [1913 Webster]
4. A thicket or jungle, often specified by the name of the prevailing plant; as, oak scrub, palmetto scrub, etc. [1913 Webster]
5. (Stock Breeding) One of the common live stock of a region of no particular breed or not of pure breed, esp. when inferior in size, etc. [U.S.] [1913 Webster]
6. Vegetation of inferior quality, though sometimes thick and impenetrable, growing in poor soil or in sand; also, brush; -- called also scrub brush. See Brush, above. [Australia & South Africa] [Webster 1913 Suppl. +PJC]
7. (Forestry) A low, straggling tree of inferior quality. [Webster 1913 Suppl.]
Scrub bird (Zool.), an Australian passerine bird of the family Atrichornithidae, as Atrichia clamosa; -- called also brush bird.
Scrub oak (Bot.), the popular name of several dwarfish species of oak. The scrub oak of New England and the Middle States is Quercus ilicifolia, a scraggy shrub; that of the Southern States is a small tree ({Quercus Catesbaei}); that of the Rocky Mountain region is {Quercus undulata}, var. Gambelii.
Scrub robin (Zool.), an Australian singing bird of the genus Drymodes. [1913 Webster]