In the minor illusion spell it defines it's image object must be
[...] no larger than a 5-foot cube.
This can potentially be interpreted in two ways:
- 125 cubed feet of object (must have a volume strictly less or equal to 5ft x 5ft x 5ft)
- No larger than 5ft in any dimension (must fit in a 5ft cube without any transformation)
Which is correct?
As a potential counter example to #2 being the relevant definition, the Teleport spell has the specific restriction that
[...] If you target an object, it must be able to fit enlirely inside a 10 foot cube [...]
which is a very different phrasing to
[...] is no larger than a 5-foot cube [...]