Definition of "improper"

unsuitable to needs or circumstances; inappropriate; inapt  examples

Not in keeping with conventional mores or good manners; indecent or immodest  examples

Not according to facts; inaccurate or erroneous  examples

Not consistent with established facts; incorrect  examples

Not properly named; See, for example, improper fraction  examples

(obsolete) Not specific or appropriate to individuals; general; common.  quotations

(mathematics) Of a complex random variable, correlated with its conjugate  examples

(obsolete, transitive) To appropriate; to limit.  quotations

(obsolete) To behave improperly