'Quality time' (QT) is an informal reference to time spent with loved ones (e.g., close family, partners or friends) which is in some way important, special, productive or profitable. It is time that is set aside for paying full and undivided attention to the person or matter at hand. It may also refer to time spent performing some favorite activity.
"Quality time" (noun phrase) is a relatively new expression. Strictly speaking, a word which defines the nature of, or that modifies, a noun would be an adjective, and the adjectival form of the word quality is qualitative. However, the expression "quality time" has become the more usual expression since the 1970s. One of the earliest records of this phrase in print was in the Maryland (USA) newspaper The Capital, January 1973, in the article "How To Be Liberated":
The major goal of each of these role changes is to give a woman time to herself, Ms. Burton explained. "A woman's right and responsibility is to be self fulfilling," she said. She gives "quality time" rather than "quantity time" to each task, whether it be writing, cleaning the house or tending the children.