Relay.lib in LTspice - Explanation of Paramaters
COFF -- looks like the capacitance across the relay contacts.
LCOIL -- the inductance of the relay coil.
RCOIL -- the DC resistance of the relay coil.
ROFF -- the resistance across open relay contacts. Not infinite because that's how it goes in circuit simulation. (Infinity might cause mathematical problems.) Use a very large resistance that is big enough for your application, but not too large. It looks like this file uses 1 gigohm or 1 teraohm.
RON -- the resistance through closed relay contacts. Not zero for the same reason as above. Don't make it unreasonably small. Huge differences between Ron and Roff may sometimes cause simulation problems.
INOM -- nominal coil current. Inom is calculated, not user-specified, so leave it alone.
VNOM -- nominal coil voltage (e.g., 5V for a relay with a 5V coil)
VON -- seems to be a percentage; maybe it is the fraction of nominal voltage that actually activates the relay. VOFF -- seems to be a percentage; maybe it is the fraction of nominal voltage that would let the relay release.
VH -- half the difference between Von and Voff, so it represents something akin to "hysteresis" about the nominal trip point. Again, it seems to be a unit-less percentage, not an actual voltage in volts. It is calculated, so you shouldn't set it unless you need to override.
TON -- probably a time-constant, my guess is it is how long the relay takes to close when power is applied to the coil.
.PARAM INOM=VNOM/RCOIL .PARAM VT=(VON+VOFF)/2 .PARAM VH=(VON-VOFF)/2