Step 1: Background of Sangam society.
Sangam literature provides valuable information about the social and economic structure of early Tamil society. Different groups were identified by their occupation and status.
Step 2: Meaning of Vellalar.
The term “Vellalar” referred to wealthy and influential large landowners who controlled agricultural production and enjoyed high social status in Sangam society. They were distinct from ordinary peasants and laborers.
Step 3: Conclusion.
Therefore, in Tamil Sangam literature, Vellalar were identified as large landowners.
\[
\boxed{\text{Large landowners}}
\]