【求助】投稿说明中一句话的意思

这是投稿说明中关于title的要求
第四条a running title我不明白，第一条不是已经讲到标题了吗？那这个running title指什么呢
谢谢指点

The Title page should include (1) a short and informative full article
title (series titles are not accepted); (2) names of all authors
(with one forename in full for each author), followed by their affiliations
(department, institution, city with postcode, country);
(3) the mailing address, fax and phone number and e-mail
address of the corresponding author; (4) a running title of 50 characters
or less.