a thorny weed or brier: the wild, prickly scrub that overruns neglected ground
This word names the thorny brush that springs up wherever farmland is left to itself. It belongs almost entirely to the book of Isaiah, where it works as a set phrase: it is nearly always yoked to a companion word for wild brush (שַׁיִת), and once it stands beside another common thorn word (קוֹץ). Together they draw one picture, a vineyard or field gone to ruin, its careful rows swallowed by scrub.
In Isaiah the thorns carry more than a farmer's complaint. They stand for a land under judgment that God has stopped tending (Isaiah 5:6; 7:23-25; 32:13), and for the wickedness and enemies that God's fire will burn away in a single day (Isaiah 9:18; 10:17; 27:4). The plant is worthless and unwanted, fit only to be cleared off or consumed.
Which exact species stands behind the word is unknown. English "briers" or "thorns" carries the general sense well: useless, prickly growth that marks a place as abandoned.