What does it mean to "Love Our Neighbour"?

References:Believers Bible Commentary William MacDonaldTyndale New Testament Commentaries Mark - R. Alan ColeThe Bible Exposition Commentary vol.1 Warren W. WiersbeThe New International Commentary on the New Testament The Gospel of Mark William L. LaneStudies in the Four Gospels G. Campbell MorganArticle - Love your neighbour as yourself Mark 12:31