In Biblical times, years too were counted by sevens, with the last year of every seven being a Sabbath year:
For six years you are to sow your fields and harvest the crops, but during the seventh year let the land lie unplowed and unused. Then the poor among your people may get food from it, and the wild animals may eat what they leave. Do the same with your vineyard and your olive grove.
When you enter the land I am going to give you, the land itself must observe a sabbath to the LORD. For six years sow your fields, and for six years prune your vineyards and gather their crops. But in the seventh year the land is to have a sabbath of rest, a sabbath to the LORD. Do not sow your fields or prune your vineyards. Do not reap what grows of itself or harvest the grapes of your untended vines. The land is to have a year of rest. Whatever the land yields during the sabbath year will be food for you—for yourself, your manservant and maidservant, and the hired worker and temporary resident who live among you, as well as for your livestock and the wild animals in your land. Whatever the land produces may be eaten.
You may ask, “What will we eat in the seventh year if we do not plant or harvest our crops?” I will send you such a blessing in the sixth year that the land will yield enough for three years. While you plant during the eighth year, you will eat from the old crop and will continue to eat from it until the harvest of the ninth year comes in.
When the neighboring peoples bring merchandise or grain to sell on the Sabbath, we will not buy from them on the Sabbath or on any holy day. Every seventh year we will forgo working the land and will cancel all debts.