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A Balmer-break galaxy (BBG) is a galaxy identified as star forming by a relative lack of radiation with rest wavelength (i.e., adjusted for redshift) shorter than 3646 angstroms, the Balmer limit, the lower limit on wavelengths in the Balmer series. They are analogous to Lyman-break galaxies similarly affected by the Lyman series. This spectral feature, known as the Balmer jump, is common in A-type stars, whose presence and limited lifetime indicate recent star formation. The feature is especially useful in identifying such galaxies because it can be found not only by spectrography but by photometry using specifically-chosen color indices, even at high redshift, thus it offers a means to identify sample sets of star-forming galaxies in the distant past, such as during the peak star-formation epoch.