ratir yā saṅgamāt pūrvaṁ darśana-śravaṇādi-jā tayor unmīlati prājñaiḥ pūrva-rāgaḥ sa ucyate

When attachment produced in both the lover and beloved before their meeting by seeing, hearing and so on becomes very palatable by the mixture of four ingredients, such as vibhava and anubhava, this is called purva-raga.