There's never a short answer to an SEC question, but in this case it means that the S-3 Registration Statement has effectively registered the $150M in investment vehicles that appear on it (https://www.sec.gov/Archives/edgar/data/1379006/000110465920037812/tm2013340-1_s3.htm). The SEC makes a Declaration of Effectiveness...the Company doesn't.
Snippets from people that know about S-3s: "The advantage of this type of structure is that, once an issuer has an effective shelf registration statement, there is no delay in waiting for the SEC to review the prospectus or the terms of the offering. Unlike a posteffective amendment, the prospectus supplement does not have to be declared effective by the Staff. In addition, the Staff historically has been less likely to review the initial filing of a shelf registration statement on Form S-3 or Form F-3 than other forms of registration statements. Accordingly, it is usually more time-efficient and cost-efficient to register securities using a shelf registration statement."