term for data that compares a day to same day of a week/month/year ago
A repeated cross-sectional study. Cross-sectional refers to data collected at one specific point in time or over a short period. Repeated since you compare at least two time frames. If there are several time frames, one could talk about time-series cross-sectional (TSCS) data. Repeated cross-sectional studies may become pseudolongitudinal, or longitudinal if carried over a longer lapse of time.