Source : Webster's Revised Unabridged Dictionary (1913)

Imperfect \Im*per"fect\, a. [L. imperfectus: pref. im- not +
   perfectus perfect: cf. F imparfait, whence OE. imparfit. See
   {Perfect}.]
   1. Not perfect; not complete in all its parts; wanting a
      part; deective; deficient.

            Something he left imperfect in the state. --Shak.

            Why, then, your other senses grow imperfect. --Shak.

   2. Wanting in some elementary organ that is essential to
      successful or normal activity.

            He . . . stammered like a child, or an amazed,
            imperfect person.                     --Jer. Taylor.

   3. Not fulfilling its design; not realizing an ideal; not
      conformed to a standard or rule; not satisfying the taste
      or conscience; esthetically or morally defective.

            Nothing imperfect or deficient left Of all that he
            created.                              --Milton.

            Then say not man's imperfect, Heaven in fault; Say
            rather, man's as perfect as he ought. --Pope.

   {Imperfect arch}, an arch of less than a semicircle; a skew
      arch.

   {Imperfect cadence} (Mus.), one not ending with the tonic,
      but with the dominant or some other chord; one not giving
      complete rest; a half close.

   {Imperfect consonances} (Mus.), chords like the third and
      sixth, whose ratios are less simple than those of the
      fifth and forth.

   {Imperfect flower} (Bot.), a flower wanting either stamens or
      pistils. --Gray.

   {Imperfect interval} (Mus.), one a semitone less than
      perfect; as, an imperfect fifth.

   {Imperfect number} (Math.), a number either greater or less
      than the sum of its several divisors; in the former case,
      it is called also a {defective number}; in the latter, an
      {abundant number}.

   {Imperfect obligations} (Law), obligations as of charity or
      gratitude, which cannot be enforced by law.

   {Imperfect power} (Math.), a number which can not be produced
      by taking any whole number or vulgar fraction, as a
      factor, the number of times indicated by the power; thus,
      9 is a perfect square, but an imperfect cube.

   {Imperfect tense}
      (Gram), a tense expressing past time and incomplete
             action.

Source : WordNet®

imperfect tense
     n : a tense of verbs used in describing action that is on-going
         [syn: {progressive}, {progressive tense}, {imperfect}, {continuous
         tense}]