Arising from the Latin obliquus and taken from there into Middle English, this word is often defined by what it is not, rather than what it is. You’ll see this in this definition from the Collins Dictionary where ‘oblique is defined as:
“neither parallel nor at right angles to a specified or implied line”
Literally, oblique means ‘at a slant’, ‘at an angle to the upright’.
It is used metaphorically to describe something ‘out-of-left-field’, unusual, counter-to, or at odds with common or accepted practice.
Be aware that the context of this word could imply critique of the person, idea or item which is described as being ‘oblique’. Use it with full attention to its possible implications.