Hi Justin,

We're actually working on exposing better definitions right now. We've got the definitions from Morningstar and surfacing them in the documentation soon. This is in active development. So https://www.quantopian.com/help/fundamentals should have this and many other definitions soon.

Regarding your specific question, the documentation we have from Morningstar looks to define stock_type the same but includes the numbers:

The purpose of the Stock Types is to group companies according to the
underlying fundamentals of their business. They answer the question:
If I buy this stock, what kind of company am I buying? Unlike the
style box, the emphasis with the Stock Types is on income statement,
balance sheet, and cash-flow data—not price data or valuation
multiples. We focus on the company, not the stock. Morningstar
calculates this figure in-house on a monthly basis. Investors can use
the Stock Types to diversify portfolios across a variety of different
kinds of companies. They can also use the Stock Types as a benchmark
for comparing the performance of any one company against the
performance of similar companies. Finally, in analyzing companies in
different Stock Types, different questions become important. For
Cyclicals, how did the company do during the last recession? For High
Yield, how dependable is the company’s dividend? For Speculative
Growth, how much cash does the company have to spend to generate its
rapid revenue growth? We divide the universe into eight Stock Types.
There’s nothing magical about eight; we simply broke out companies the
way we tend to think about them when analyzing them. (There are some
stocks that don’t have enough data to assign a Stock Type. These are
labeled N/A.) Also, a stock may meet the conditions for more than one
Stock Type. We designed the algorithm, however, so that it will assign
only one Stock Type per stock—the Stock Type we feel is most
appropriate. The 8 stock types are:Aggressive Growth-1: companies
whose sales and earnings have grown very rapidly over the trailing
five-year period. These firms tend to be a step up the quality ladder
from speculative-growth firms. Classic Growth-2: companies that show
moderate to rapid growth over the trailing five-year period in two of
the following three categories: sales, earnings, dividends. These tend
to be fairly mature firms, but ones that are still generating steady
growth. Cyclicals-3: companies whose core business can be expected to
fluctuate in line with the overall economy. In a booming economy such
companies will look excellent; in a recession, their growth stalls and
they might even lose money. orningstar, Inc. Global Equity Data
Fundamentals Confidential Questions: 1-800-775-8118 or
[email protected] 7 Distressed-4: companies that
are having serious operating problems. This could mean declining cash
flow, negative earnings, high debt, or some combination of these. Such
“turnaround” stocks tend to be highly risky, but also harbor some
intriguing investments. Hard Asset-5: companies whose main business
revolves around the ownership or exploitation of hard assets like real
estate, metals, timber, etc. Such companies typically sport a low
correlation with the overall stock market, and have traditionally been
where investors look for inflation hedges. High Yield-6: companies
whose stocks offer a high dividend yield. These tend to be mature
companies that choose not to reinvest the bulk of their earnings. For
investors interested in income, this is where to look. Slow Growth-7:
companies that have grown slowly, if at all, over the trailing
five-year period. These companies tend to be mature firms. Speculative
Growth-8: companies whose sales have grown very rapidly over the
trailing five-year period, but whose earnings growth has been spotty.
These tend to be companies in the early phase of their growth cycle.

OK, let me clean up that formatting for you:

Aggressive Growth-1
Classic Growth-2
Cyclicals-3
Distressed-4
Hard Asset-5
High Yield-6
Slow Growth-7
Growth-8

Cheers, Thanks Josh!

To close the loop on this thread, the fundamentals detail page has been updated with definitions from Morningstar's document. It was done in an automated fashion so if there are quirks, definitely let me know and we can manually override and fix the definitions.

https://www.quantopian.com/help/fundamentals