Nitya karma refers to those karmas (or rituals) which have to be performed daily by Hindus[according to whom?]. The Hindu Shastras[which?] say that not performing nitya karmas leads to sin. The nitya karmas include:
Nitya Karma does not necessarily mean daily duties. It includes any regular/periodic scheduled activities/duties. E.g.: Amavasya tharpanam, Grahana tharpanam, Pithru devasam.
There is a subdivision of Nithya karma which is called Nai-Nithya karma. This means compulsory karma but conditional. E.g. Grahana related karmas