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An acquired defect of cellular immunity associated with infection by the human immunodeficiency virus (HIV), a CD4-positive T-lymphocyte count under 200 cells/microliter or less than 14% of total lymphocytes, and increased susceptibility to opportunistic infections and malignant neoplasms. Clinical manifestations also include emaciation (wasting) and dementia. These elements reflect criteria for AIDS as defined by the CDC in 1993.

Engl. law. Formerly they were certain sums of money granted by the tenant to his lord in times of difficulty and distress, but, as usual in such cases, what was received as a gratuity by the rich and powerful from the weak and poor, was soon claimed as a matter of right; and aids became a species of tax to be paid by the tenant to his lord, in these cases: 1. To ransom the lord's person, when taken priisoner; 2. To make the lord's eldest son a knight; – 3. To marry the lord's eldest daughter, by giving her a suitable portion. The first of these remained uncertain; the other two were fixed by act of parliament at twenty shillings each being the supposed twentieth part of a knight's fee, 2 Bl. Com. 64.