What it means to take 'The Fifth'

Lois Lerner, the head of the IRS unit handling tax-exempt status, invoked her Fifth Amendment right against self-incrimination before the House Oversight Committee on Wednesday.
She is in the spotlight following a Treasury inspector general's report that found her unit used political criteria to screen applications for tax-exempt status from tea party and other conservative organizations.
Lerner joins a long line of officials who "took the Fifth" when called to testify before Congress.