Yeast slurry is part of the trub at the bottom of the carboy in any fermentation. It includes: yeast, hop particles, and any other break material that precipitates to the bottom.
I checked the website
Skeeter Pee, to get the recipe. It sounds like this fella is making what most of us call Hooch, his just happens to be lemon hooch.
What he means is, pitch a whole lotta yeast because you are adding 7 lbs of sugar to lemon juice. That means, a very high OG and a very low pH. Yeast will be seriously stressed in that kind of environment even with the added yeast nutrients and "energizer" (whatever that is)
What I think he means by
yeast slurry, is pitching a huge population of yeast, most easily obtained from the trub of a previous batch of beer or wine. What I would advise you to do, is make a huge yeast starter, comparable to your OG by using this calculator
Mr Malty. My guess, is that you will need to make at least a gallon starter to overcome the large gravity from the table sugar and the low pH from the lemon juice.
Good luck.
-Jeff-