* Good: This is the most common meaning. It's the equivalent of "good" in English. For example, "Nallathu oru pattu" (നല്ലത് ഒരു പാട്ട്) means "It's a good song."
* Nice: Similar to "good," but with a slightly more positive connotation. It can also mean "pleasant." For example, "Nallathu kaalavum" (നല്ലത് കാലവും) means "It's a nice day."
* Well: This meaning refers to a state of good health or feeling. For example, "Nallathu thanne" (നല്ലത് തന്നെ) means "I'm fine."
The exact meaning of "nallathu" will depend on the context of the sentence. If you can provide me with the full sentence, I can give you a more accurate translation.