The phrase Deep Survey is used for Surveys carrying out lengthy observations to identify very distant phenomena, e.g., galaxies and Quasars at high Redshift. The observation time can be days or more, typically focused on a region (called a Deep Field) of no more than a square degree, often much less. A field may be devised for the survey or the survey may reuse an existing deep field, e.g., to explore it in more depth or in a different part of the EMR spectrum, or to use Spectrography.
Spitzer Extended Deep Survey (SEDS)
Subaru XMM-Newton Deep Survey (SXDS)
VIRMOS-VLT Deep Survey (VVDS)