COPY can read/write data not only from/to CSV, but also from/to binary files. For the import, the table must exist along with its columns matching CSV columns.
COPY <table> TO 'file.csv' DELIMITER ',' CSV HEADER;
COPY (SELECT <column1>,<column2> FROM <table>) TO '<file>.csv' CSV;
COPY <table> TO 'file.csv' DELIMITER ',' CSV HEADER NULL as E'';
COPY <table> FROM '<path>/<file>.csv' DELIMITER ',' CSV;
COPY <table>("<column1>", "<column2>") FROM '<file>.csv' DELIMITER ',' CSV;
COPY <table> FROM '<file>.csv' DELIMITER E'\t' CSV;
cat myfile | psql -c "COPY <table> FROM STDIN"