1st表示的是单词first，是序数词“第一”的意思。
序数词是数词的一种，主要在英语语法中讲到，在汉语中表示为“第几”。此外，在生日中，描述你出生的日期时，也用到了序数词。比如：May first （5月1日）
其他序数词：first (1st) second (2nd) third (3rd) fourth (4th) fifth (5th)
sixth (6th) seventh (7th) eighth (8th) ninth (9th) tenth (10th) eleventh (11th) twelfth(12th) thirteenth (13th) fourteen (14th) fifteenth (15th) sixteenth (16th) seventeen (17th) eighteenth (18th) nineteenth (19th) twentieth (20th) twenty-first (21st) thirtieth (30th) thirty-ninth(39th) fortieth (40th) fiftieth (50th) sixtieth (60th) seventieth (70th) eightieth (80th) ninetieth (90th) hundredth (100th) one hundryed-first(101th)
