See the latest recommendations from the Survey Cadence Optimization Committee, in Project Science Tech Note PSTN-055.
The main survey (see question above) of Rubin Observatory is sometimes referred to as the Wide Fast Deep survey, reflecting the observing objectives of the survey design.
Review Survey Cadence Optimization Committee's Phase 2 Recommendations. Also, see the overview of survey observing strategy.
Mini-surveys are portions of the sky that will be observed with a different cadence than the main survey, but not necessarily to a greater depth, to address science goals beyond the scope of the main survey, such as coverage of the Galactic Plane, Ecliptic, or South Pole. See the overview of survey observing strategy.
Deep Drilling Fields (DDF) are single pointings (aside from dithering). They will be visited with a different cadence, producing a longer-term deeper cumulative depth. There will be at least 5 DDF, depending on how much time is required by the main survey to accomplish the main LSST goals, and how much time is spent on mini-surveys. See the latest recommendations for DDFs and mini-surveys from the Survey Cadence Optimization Committee, in Project Science Tech Note PSTN-055.
Four DDF fields have already been selected. There will be between 5 and 10 DDF, depending on how much time is required by the main survey to accomplish the main LSST goals and how much time is spent on Mini-surveys.
