Manuka honey comes from the leptospermum family of plants known in Australia and New Zealand as either manuka, teatree or jellybush.
Typically it has a rich, malty flavour;  a dark amber colour and thick,  creamy texture. And it famously can have strong anti-bacterial properties.
These are usually shown on the label by a + (i.e. plus) symbol.
There are two different potency rating systems used on manuka honey labels - MGO and UMF.
MGO ratings show how much of the active natural ingredient - methylglyoxal, is in each kilogram of the honey. (e.g. 100+ means 100mgs per kg). MGO ratings range from 30 to as high as 900.
UMF (i.e Unique Manuka Factor) ratings show the phenol bleach solution equivalence of the honey. (So UMF 5 is equivalent to a 5% phenol bleach solution). UMF ratings range from a minimum of 5 to a maximum of 25.