Illam

Illam () is a Malayalam word for a house of a Namboodiri. Synonym for 'Illam' is 'Mana'. This is a Malayalee lineage system used for classification and identification of homes based on castes in Kerala, South India. The system is most notably used by the Namboodiris.
The Namboodiris, who are the Brahmins of Kerala, also refer to their lineages as the Brahmaalayam or Mana. The line is built according to the canons of Vaasthusaasthram, meaning architecture in the Sanskrit language.
The traditional layout of a Namboodiri illam is an open courtyard in the middle called the 'nadumittam'. 'Nadu' meaning middle and 'mittam' meaning earth/ground. These buildings or houses are in different category like 'nalukettu' (meaning courtyard surrounded by rooms on four sides ), 'ettukettu' ( nalukettu surrounded by another nalukettu) then 'pathinarukettu' ( four layers of buildings around a courtyard). 
References.
https://www.namboothiri.com/articles/illam.htm
https://www.keralatourism.org/destination/poonthanam-illam-kizhattoor-perinthalmanna/393