What does it mean if my blood pressure reading is high?

One high reading does not diagnose you as hypertensive (having high blood pressure).  Many factors will raise your blood pressure, such as standing, activity level, or stress, among others.  If a blood pressure reading is high, it is recommended to sit quietly for 5-10 minutes and re-assess.  If the reading remains high, it is suggested to have your blood pressure checked by your physician.
Multiple, high readings would need to be recorded by your physician on consecutive days under resting conditions before you would be diagnosed as hypertensive.