For backups produced with mysqldump --tab, each table is represented in the output directory by an .sql file containing the CREATE TABLE statement for the table, and a .txt file containing the table data. To reload a table, first change location into the output directory. Then process the .sql file with mysql to create an empty table and process the .txt file to load the data into the table:

$> mysql db1 < t1.sql
$> mysqlimport db1 t1.txt

An alternative to using mysqlimport to load the data file is to use the LOAD DATA statement from within the mysql client:

mysql> USE db1;
mysql> LOAD DATA INFILE 't1.txt' INTO TABLE t1;

If you used any data-formatting options with mysqldump when you initially dumped the table, you must use the same options with mysqlimport or LOAD DATA to ensure proper interpretation of the data file contents:

$> mysqlimport --fields-terminated-by=,
         --fields-enclosed-by='"' --lines-terminated-by=0x0d0a db1 t1.txt

Or:

mysql> USE db1;
mysql> LOAD DATA INFILE 't1.txt' INTO TABLE t1
       FIELDS TERMINATED BY ',' FIELDS ENCLOSED BY '"'
       LINES TERMINATED BY '\r\n';