Ensanche means "widening" in Spanish. It is used to name the development areas of Spanish cities around the end of the 19th century, when the demographic explosion and the Industrial Revolution

Industrial Revolution

The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...

 prompted the tearing down of the old city wall and the construction of neighborhoods under grid plan

Grid plan

The grid plan, grid street plan or gridiron plan is a type of city plan in which streets run at right angles to each other, forming a grid...

s.

The program of city extensions in Spain began simultaneously in 1860 with the plans for Barcelona by Ildefons Cerdá and Madrid by Carlos Maria de Castro, influenced by Haussmann's transformation of Paris from 1852 (and, in turn, have been said to have influenced Haussmann's later projects). Those ensanches extended cities beyond their traditional limits by demolishing city walls, transforming riverbanks and subdividing the "extramuros" – rural land outside the city walls. Ensanches were generally based on principles articulated by Cerdá. These included reserving significant open space by requiring mid-block open space and whole block parks. The height of buildings was set by reference to the width of the adjacent street. Many of these requirements were modified, and the building volumes increased, by later amendments beginning in 1864 (Madrid).

It is specifically used for:

• The Eixample
  Eixample
  The Eixample is a district of Barcelona between the old city and what were once surrounding small towns , constructed in the 19th and early 20th centuries....
  
  (Catalan for "ensanche") of Barcelona, planned by Ildefonso Cerdá.
• The Ensanche Este of Madrid
  Madrid
  Madrid is the capital and largest city of Spain. The population of the city is roughly 3.3 million and the entire population of the Madrid metropolitan area is calculated to be 6.271 million. It is the third largest city in the European Union, after London and Berlin, and its metropolitan...
  
   under the Plan Castro by Carlos Maria de Castro enacted by Royal Decree in 1860.
• The Ensanche of Bilbao
  Bilbao
  Bilbao ) is a Spanish municipality, capital of the province of Biscay, in the autonomous community of the Basque Country. With a population of 353,187 , it is the largest city of its autonomous community and the tenth largest in Spain...
  
   after the annexation of the former village of Abando
  Abando
  ----Abando was the name of an old municipality of Biscay , that was eventually absorbed by Bilbao. Nowadays, the name refers to the central district and neighbourhood of this city, holding the provincial administration, the long-distance RENFE Bilbao-Abando train station, three subway stations ,...
  
  .