Worksheet with column and row titles.
When you enter data, it's a good idea to start by entering titles at the top of each column so that anyone who shares your worksheet can understand what the data means (and so that you can understand it yourself, later on).
In the picture, the column titles are the months of the year, across the top of the worksheet.
You'll often want to enter row titles too. In the picture, the row titles down the left side are the names of companies.
This worksheet shows whether or not a representative from each company attended a monthly business lunch.