starter weight

In baker's math the total weight of FLOUR is 100%. Everything else is referenced to it. In this case, 166% Starter weighs 1.66 times the weight of the recipe's (formula's) total flour.

Unfortunately, there is no one common practice to include starter in a formula. Some bakers (perhaps a majority) just list the starter's weight referenced to the total flour's weight, as in your example. For completeness, the starter's hydration % must be known also.

If you're not familiar with Hydration % that's the ratio of a Total Liquid(s) weight to Total Flour Weight x 100: more Baker's Math.

Other bakers list the starter's flour weight and water weight seperately. By doing that with the formula's final dough weight, and hydration % everything else (flour, water, salt, etc.) can be easily calculated.

If you don't already know baker's math--and your question implies you don't--I strongly suggest you learn it. It's how most bakers communicate the details of a formula (recipe). There are many references here on TFL. Use the search facility on the left-hand side.

Also, Dan DiMuzio's recent book, bread baking, An Artisan's Perspective, has an entire chapter devoted to Baker's Math, with in-depth explanations why it's so useful, supporting examples, and "homework" assignments.

David G

http://www.thefreshloaf.com/handbook/baker039s-math

http://www.thefreshloaf.com/node/15217/bread-dough-formula-math-dilemma-some-help-i-hope