An edge filter is an optical component, which blocks the light in a defined spectral range, but let it through in an adjacent range with high transparency.
In case the wavelength of the transmission range is longer than in the blocking zone, we talk about a long pass filter (long-wave pass filter or cut-on), conversely it is a short pass filter (short-wave pass filter or cut-off). The blocking can be produced by absorption e.g. with coloured glasses or by reflection. For the blocking by reflexion suitable interference layer systems are used.

Short pass filter with edge @λ 494nm (blue filter)