An equivocal plea is one that is contradictory, where the defendant pleads guilty, but adds something that indicates a defence. A good barometer of whether a plea is equivocal is if it can be described as ‘guilty, but…’
That said, it may be that the statement that follows the plea indicates that the defendant does not accept that they are guilty, but is pleading simply for convenience.
Simple examples may be, ‘I plead guilty, but I didn’t do it’, ‘I plead guilty but it was in self defence’ or ‘I just want it over and done with’.
Upon a conviction, it is possible to ask the Crown Court or Court of Appeal to vacate the defendant’s plea of guilty on the basis that it was equivocal. This will then require the court to send the case back to the Magistrates’ Court for the defendant to enter a not guilty plea.