The lightsaber, sometimes referred to as a laser sword, is a weapon used by the Jedi, the Sith, and other Force-sensitives. Lightsabers consist of a plasma blade, powered by a kyber crystal, that is emitted from a usually metal hilt and can be shut off at will.
An article (abbreviated ART) is a word (or prefix or suffix) that is used with a noun to indicate the type of reference being made by the noun.
The rule always applies to the sound, not the orthographic representation of the letter. Thus, it'd be 'an NGO.' Likewise, not all vowels use 'an' as an article. For example: a one-time, a united... To help you confirm in the future, try out s...