There are three basic units in any table: the table itself, the table row, and the table cell. The tags for these are:

Table: <table>

Table row: <tr>

Table cell: <td>

Why do table cells have tags called <td> instead of <tc>? Just to make things more confusing. The tag actually stands for "table data,".

The thing to remember here is that a <td> is always enclosed in a <tr>, which is always enclosed in a <table>.