Wiktionary
n. A Japanese novel primarily targeting young adults, typically illustrated and containing not more than 50,000 words.
Wikipedia
A is a style of Japanese novel primarily targeting middle- and high-school students ( young adult demographic). "Light novel" is a wasei-eigo, or a Japanese term formed from words in the English language. Such short, light novels are often called or LN in the West. They are typically not more than 40,000–50,000 words long (the shorter ones being equivalent to a novella in US publishing terms), are rarely more than a few hundred pages, often have dense publishing schedules, are usually published in bunkobon size ( A6, 10.5 cm × 14.8 cm), and are often illustrated. The text is often serialized in anthology magazines before collection in book form.
Usage examples of "light novel".
Kramer could not imagine anything more wildly improbable in the world than that the man whose combat operation he had betrayed should bring him a box of chocolates, bunch of flowers, light novel or whatever else was appropriate.
But I had deciphered from upside down the title of the book she was reading: it was a light novel.
If the situation is false, you cannot even accept it as a light novel, for there is no story for the light novel to be about.