The Cave of Adullam was originally a stronghold referred to in the Old Testament, near the town of Adullam, in which David, already anointed to succeed Saul as king, sought refuge from the latter. The word "cave" is usually used but "fortress", which has a similar appearance in writing, is used as well. Given that this was a bandits' hideout, it would be reasonable to describe this as a fortified cave.
During this period, David passed up several opportunities to kill Saul, who in turn was attempting to kill his young rival, whose followers believed had been chosen by God to succeed King Saul. David refused to fight unfairly, for instance by killing the bellicose Saul in his sleep. According to the Old Testament God honored David's high ethical standards, and soon King David and his Mighty Men who had once hidden in the Cave of Adullam, were renowned throughout Israel for their deeds of valor.
The term "Cave of Adullam" has been used by political commentators referring to any small group remote from power but planning to return. Thus in Walter Scott's 1814 novel Waverley when the Jacobite rising of 1745 marches south through England, the Jacobite Baron of Bradwardine welcomes scanty recruits while remarking that they closely resemble David's followers at the Cave of Adullam; "videlicet, every one that was in distress, and every one that was in debt, and every one that was discontented".
Speak to me, speak to me in my cave of Adullam.
Reach to me, reach to me.
No one cares for my soul.
I thought I saw your kingdom,
but it's not going to happen like I thought it would happen.
Remind me, remind me of the vision you gave me.
Remind me, remind me what anointing oil is for.
I need to know you're near me.
I need to know you are holding me just as closely
Chorus: as the day you took my life and gave me a vision,
as the day you poured the oil and gave me a dream.
I can't believe this is happening.