VWAP is volume weighted average price.
Trend Day is a large move day in market. A bullish trend day starts at the low of the day and ends at the high of the day and vise versa .
Trend Day VWAP is a important reference, for a bullish trend day; its VWAP acts as support if next day prices are trading above it.
For a Bearish trend day, its VWAP acts as a resistance if next day the prices are trading below it.
Why is the trend day and its VWAP so important together ?
Trend days are usually signs of a big directional bet taken by market and to protect its average cost is the work of the buyer / seller and hence its important for the trend in itself to hold.
Example - VWAP of 29th Oct on BNF which acted as support on 30th Oct in BNF Nov Future contract.
This can be applied in any contract with the same logic.
Disclaimer: - Link & above taken chart is just a example, not to be taken as a reco to buy / sell