Continuous pagination is simply the idea that throughout a series of issues the page numbers grow steadily. Most often this is true within a single volume of an academic journal. For example, if the journal appears quarterly and averages 128 pages per issue, the issues would be as follows:
Issue 1 = pages 1-128
Issue 2 = pages 129-256
Issue 3 = pages 257-384
Issue 4 = pages 385-512
The next issue, issue 1 of the next volume, would start over again at page 1. If a journal is numbered in this way, the reader doesn't need to know the issue number since it is clear from the page number where in the volume the item will appear (and for that reason the issue number is typically left out of the citation.
Contrast that situation with the case of a journal that starts its page numbering over with each issue (as is true of most newspapers and popular magazines). In that case, the reader needs to know either the issue number or the date (if given) in order to know (for example) which of many page 14's a given article appears on.