The term seed refers to the internal value SQL Server uses to generate the next value in the sequence. By default, an identity column’s first value is 1 and each new value increments by one (1, 2, 3, 4, and so on).
You can control the column’s first and subsequent values, by specifying those values when you create the column. For instance, you might want to begin with a purchase order number of 1001 rather than 1.
Once the table’s in production you can reset, or reseed the column. In other words, you can change the column’s seed value at any time. For instance, you might reseed a column after deleting records or moving data to an archive table.
The good news is that seeding and reseeding an identity column is easy and relatively safe, if you do it correctly. It’s common to seed a new table or to reseed a production, but empty table. However, as a general rule, it’s not a great idea to reseed an identity column in a table that contains data without some serious checks and balances.