The query looks at the most recent gift year (not necessarily including this year) and then counts consecutive years backwards, based on filter criteria ( like gift types). The query reviews the most recent stretch of giving.
A Constituent's most recent gift was 12/17/02, and had gifts dating back each calendar year to 1991. This gave them 10 years consecutive giving, counting backward from the date of their most recent gift. So, in the same scenario, if this Constituent then had gifts in 2010 and 2009, they would not be in the query results, because their most recent gift was 2010, and going back from that date, they do not have 10 consecutive years.