Lar Familiaris
Within the Roman pantheon, the Lares are protecting spirits of place who may protect the inhabitants of their regional domain if regular offerings are made to them. There are a number of kinds of Lares, including the Lares Familiares (guardians of the home), the Lares Compitales (guardians of the crossroads) and the Lares Praestites (guardians of the state).
Lares Familiares
The most well known Lares are the Lares Familiares - the guardian deities who protect the household and its members. They are commonly appealed to for the safety and prosperity of the household.
The origins of the Lares are unclear, some may be considered to be descended from Gods (for example, the Lares Compitales are, according to Ovid, descended from Mercury) and/or nymphs (regional nature spirits), while others may be considered to be ancestors of the people who traditionally lived on the land over which the Lares guard. Either way, the Lares are intricately tied up with their particular geographic regions - in ancient Rome the Lares connected with property were implicitly sold upon the sale of the property over which they watched.
The shrine to the Lares, now conventionally called a lararium, is often a focal point for the Religio Romana. Offerings to the Lares should be made at least once a month on the kalends, if not also on the ides and the nones. Many people make offerings daily.