what is unabsorbed depreciation?

Depreciation is a dininishing to the asset,for ex:car purchased in first year after 2 or 3 years its stamina and capacity will reduce automatically it is nothing but deprecaiation .For this Companies act schedule xiv describing the assets life for different assets.

Thanks...

If the partnership firm has been unable to file any income tax returns since its incorporation, it may not be able to claim the unabsorbed depreciation now. The ability to carry forward and claim unabsorbed depreciation typically requires the filing of income tax returns within the specified timeframes. 

 If any firms did not take depreciation in the previous itr by mistake  ....... are they able to get it now such unabsorbed  depreciation ................ ............  ??