E27

This refers to the type and size of a light globe base.

E27 is the most common type of Edison Screw base, It is often refereed to as just ES.
The number '27' refers to the diameter.

This type of base is also compatible with Compact Fluorescent Globes

See the table below for more details.

Type  Volts  Size   Name  
E05 E5018 ≤1805 mmLilliput Edison Screw (LES)
E10030 ≤3010 mmMiniature Edison Screw (MES)
E11120/240 240/12011 mmMini-Candelabra Edison Screw (mini-can)
E1212012 mmCandelabra Edison Screw (CES)
E1424014 mmSmall Edison Screw (SES)
E1712017 mmIntermediate Edison Screw (IES)
E2612026 mm[Medium] (one-inch) Edison Screw (ES or MES)
E2724027 mm[Medium] Edison Screw (ES)
E3912039 mm(Mogul) Giant Edison Screw (GES)
E4024040 mm(Mogul) Giant Edison Screw (GES)