A decimal is a fractional number and is indicated by digits after a period which is called a decimal point.
Tenths have one digit after the decimal point. The decimal 0.8 is pronounced as eight tenths.
Hundredths have two digits after the decimal point. The decimal 0.06 is pronounced as six hundredths.
Thousandths follow a similar pattern. They have three digits after the decimal point. The decimal 0.005 is pronounced as five thousandths.
Hence, five thousandths is 0.005.