Would be grateful if anybody could explain what splash damage is and how it works. Many thanks.

"Splash Damage" represents units' ability to damage multiple targets.

When you use card with that ability in skirmish and any opposing unit dies (because attack equals or exceeds enemy health), Splash Damage is triggered and it kills another unit after all skirmishes are resolved (that unit may be from any skirmish, only heroes are immune, Cloaking does not protect from Splash Damage).

If multiple Splash Damage cards are triggered, the opponent must choose maximal possible number of his units to be destroyed.

You can find more details in rules book, but fell free to ask some more precise questions.

Many thanks for taking the trouble to explain. Thank you