The melting point of a hot melt is often referred to as a ring&ball temperature on technical data sheets. This is the temperature that a steel ball, carried by a film of hot melt, is no longer carried, but due to the softening of the adhesive film, the ball falls through a ring.
The melting point is thus more or less the transition phase from solid to liquid. Most hot-melt adhesives are tough and therefore do not have a single tipping point, but have a longer trajectory from plastic to liquid phase.
The melting point is important to understand the minimum tank temperature. The tank temperature will usually be set several tens of degrees celcius higher than the melting point temperature on the technical data sheet of the hot melt glue.
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