The term "lack of" means:
- there is not enough of something
- there is an insufficient amount of something or an insufficient number of things.
I could not think well because of a lack of sleep (i.e., I was too tired)
I could not pay my bills becasue of a lack of funds in my bank account (i.e., not enough money to pay my bills)
I was not elected because of a lack of support from the voters.
People were thirsty due to a lack of drinking water.
The plants died due to a lack of rain.