Richard A. Williamson v. Citrix Online, LLC, et al. (No. 2013-1130) 35 U.S.C. § 112, para. 6 allows patent applicants to draft their claims in a way that recites a function to be performed, rather than by reciting a structure that performs the function. Drafting claim limitations in this “means-plus-function” format, however, limits the scope of the limitation to only the structure, materials, or acts described in the specification as corresponding to the claimed function, and equivalents thereof. See Slip Op. at 12. Traditionally, using the term “means” in the claim limitation created a rebuttable presumption that the limitation should be treated as a means-plus-function limitation. On the other hand, the absence of the term “means” created a rebuttable presumption that the claim limitation should not be treated as a means-plus-function limitation. The presence or absence of the term “means” is not dispositive though, and courts generally look to “whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure.” Slip Op. at 14. Over the last decade, the Federal Circuit has raised the presumption that § 112, para. 6 does not apply when the word “means” is absent, noting that the presumption is “a strong one that is not readily overcome.” Slip Op. at 14. In 2011, the Federal Circuit went further, stating that the presumption that § 112, para. 6 does not apply is not overcome “without a showing that the limitation essentially is devoid of anything that can be construed as structure.” Slip Op. at 15. On June 16, 2015, the Federal Circuit, sitting en banc, reversed course, noting that the new standard is “whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure.” Slip Op. at 16. When a claim limitation lacks the word “means,” the presumption that § 112, para. 6 does not apply is overcome if the claim fails to “recite sufficiently definite structure” or recites “function without reciting sufficient structure for performing that function.” Slip Op. at 16. Applying this new standard, the Court affirmed the lower court’s ruling that a “distributed learning control module for receiving communications…” is subject to means-plus-function treatment. The Court noted that “module” is simply a substitute for the word “means,” and does not connote sufficiently definite structure to preclude means-plus-function treatment. Slip Op. at 17. The Court further noted that although the claim term included the prefix “distributed learning control,” the prefix was not sufficient to impart sufficiently definite structure. Slip Op. at 19. The Court also rejected the testimony of the patentee’s expert that one skilled in the art would be able to program a computer to perform the recited function, finding that the ability to implement the recited function does not create structure where none is disclosed. Slip Op. at 19. Having determined that the “distributed learning control module” is a means-plus-function limitation, the Court then determined that the claim was indefinite because the specification did not disclose sufficient structure corresponding to the claimed function. Specifically, the Court found that the specification did not disclose an algorithm, e.g. as a mathematical formula, in prose, or as a flowchart, that performs the function of the distributed learning control module. This case serves as an important warning to patent applicants and practitioners regarding the use of functional claim language. Practitioners wishing to avoid means-plus-function treatment should be careful to draft claims reciting clearly defined structure, and avoid using vague terms such as “module,” “unit,” “mechanism,” or “device.” As a protective measure, practitioners should draft the specification to include a disclosure of any algorithms that may correspond to functions recited in the claims. That way, even if the claim limitation is considered to be means-plus-function, the claim will not be invalid for failure to disclose sufficient structure.