When you search for Metta in Wikipedia you will find this definition:
Mettā (Pali) or maitrī (Sanskrit) means benevolence, loving-kindness, friendliness, amity,  good will, and active interest in others. It is the first of the four sublime states (Brahmavihāras) and one of the ten pāramīs of the Theravāda school of Buddhism.
In general it is the development of loving kindness for all beings. You may wonder if this is something that this is achievable to cultivate or realistic to think that one can develop such a nature, however it might be more easy to think of it as an attitude of good will and perhaps more of an invitation for us to discover and find this within ourselves. In essence it is an offering to ourselves to find love and kindness within our own being.