una salva de aplausos
According to 501 Spanish Verbs, this means thunderous applause.
It seems to me it should be save the applause.
por favor, explique
Gracias al ambos otra vez
"salva" is a substantive here. Your book is right. Is not acting as a verb. Besides, "save the applause" would be "salva el aplauso" to have that meaning in Spanish.
I personally think that the book "501 Spanish Verbs" is not worth buying, but in any case, "salva" is not a verb here, but a noun, and it also exists in English: "salvo" (a loud sound made by many people or several guns). Note the connection with "saludar" (salute).