Latent load is the half of cooling that never shows on a thermometer: the moisture that must be removed from the air, arriving with occupant respiration and outdoor-air humidity. At the coil it is literally the remainder — total cooling comes from the enthalpy drop across the coil, sensible cooling from the dry-bulb drop, and latent is Q_total − Q_sensible, paid out as condensate at the rate ṁ_da × (W_in − W_out). The example coil moving air from 25 °C / 50% RH to 13 °C / 90% RH does 4.38 kW of latent work within its 18.70 kW total and drains 6.24 litres of water per hour while doing it.
Latent capacity is why oversizing air conditioners backfires. A unit that is too large cools the air quickly and shuts off before it has run long enough to wring the moisture out — the result is a room that is cold but damp and clammy, plus extra compressor start-stop wear. ENERGY STAR is explicit that bigger is not better: size to the room, round down to the nearest stock size rather than up, and when in doubt between two sizes in a humid climate, favor the smaller one, because runtime is what buys dehumidification.