The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne cryogenic telescope that will survey the spectrum of diffuse emission from both the Milky Way and the cosmic web to probe star formation, the interstellar medium, and galaxy evolution across cosmic time. EXCLAIM's primary extragalactic science survey maps 305 deg$^2$ along the celestial equator with an R=512 spectrometer over the frequency range \nu=420-540 GHz, targeting emission of the [CII] line over redshifts 2.5Comment: 19 pages, 14 figures, will submit to MNRAS