Glera is a white wine grape varietal with Italian origins - and yes, until 2009 was typically referred to as Prosecco. Glera is a delicate grape varietal, primarily grown for use in sparkling Italian wine styles; i.e. Method Italiano - from the various Prosecco DOC and DOCG areas. It is grown mainly in the Veneto wine region of north-east Italy, traditionally in an area between Conegliano and Valdobbiadene, in the steep hills north of Treviso.
Glera is an old varietal, with its former name Prosecco being derived from the village Prosecco near Trieste, where the grape is thought to have originated. It has been proposed that it was grown in Roman times and now ranks about 6th in importance among the country's nearly 2000 indigenous grape varietals.

 

Prosecco was traditionally used as the name for both the grape varietal and the sparkling wine produced. Prosecco di Conegliano-Valdobbiadene, Prosecco di Conegliano and Prosecco di Valdobbiadene all had DOP status, and there was also an IGP zone surrounding it.
When the higher DOCG status was sought for Prosecco di Conegliano e Valdobbiadene, it became a complication that the grape (which is now grown over a larger area) and the protected designation of origin had the same name. To resolve the issue, the old synonym Glera was officially adopted for the varietal as the same time as the DOCG was approved in 2009. The change was also made to reduce the possibility of sparkling wines of other origin being labeled as 'Prosecco' by using the grape varietals name. The name change is a move along the lines of the reservation of the term 'Champagne' only for wines made in the Champagne wine region of France.
Glera is a white grape with lower acidity levels, and generally grown in warmer climates than the varietals used for Méthode Traditionnelle. Grapes with lower levels of acidity are said to be softer as a result of the lighter body feel that is sensed from the reduced grape structure. It is this softer structure that is precisely what is appreciated about Prosecco, it also carries less acidic-mouth-tang. As a result of the softer structure, Glera needs a less demanding process to infuse it with those precious bubbles.
When treated with a secondary fermentation in bottle, a grape with these softer structural elements ends up cloudy both in colour and in flavour. Using the 'Metodo Italiano' method - Prosecco is not only softer than sparkling wines made with double fermentation, it also results in a brighter style and more affordable wine.