OTTAWA -- Sen. Mike Duffy's trial on 31 charges of fraud, breach of trust and bribery begins its fifth week Monday -- an opportunity to look at the unique lexicon that's sprung up around the case.

Age Wave: A nebulous project Duffy discussed with trainer Mike Croskery to promote physical activity among baby boomers. Croskery was paid Senate funds through the Ottawa ICF contract (see below) for consulting services Duffy said he provided during exercise sessions.

Common sense: What the Crown believes should be applied when considering Mike Duffy's claim that his principal residence was in Prince Edward Island. The defence argues that the actual rules are what can be tested in court.

Insulating concrete forms: A home construction system in which concrete is poured between reinforced polystyrene foam forms; also the core product of a company (Maple Ridge Media/Ottawa ICF) to which Duffy awarded up to $65,000 in contracts for business he said was Senate-related.

Jiffy Photo: A suburban Ottawa photo developing shop that printed and mounted about $1,500 worth of photos for Duffy, paid through the Ottawa ICF contract (see above).

Mistake-repay scenario: Term coined by defence lawyer Donald Bayne; refers to alleged plan by Prime Minister's Office to force Duffy to say he had made a mistake claiming $90,000 in living expenses, and then to repay expenses, thereby helping make a political problem go away.

Oversight: For Senate human resources and finance officials, involved verifying that contract and expense forms were filled out properly; did not include making sure contract work was actually performed, or scrutinizing exactly what a senator was doing when they declared he or she was travelling on "Senate business."

Partisan activities: According to the SARs (see below), an "inherent and essential" part of a senator's parliamentary functions. All activities may or may not be eligible for Senate-paid travel, depending on how one interprets the spending guidelines.

Primary residence: a) Primary means main or usual and residence means where you live, according to the Crown. b) The place a senator designates on a form as his or her primary residence.

SARs: Not the viral respiratory disease that hit Toronto in 2003, but the "Senate "Administrative Rules." A foundational document guiding the work of senators and a favourite reference point for Bayne.

Sixty-four point travel system: Not a cheapo airline loyalty program, but the allotment senators have for expensing flights when they are more than 100 kilometres away from home. Each return flight between Ottawa and the home province counts as one point. A quarter-point is deducted for each leg of travel within a senator's home region.

Volunteer: a) a person who works without remuneration. b) a person who might receive a cheque for $500 as a thank-you for their free work, as did Duffy office figure Ashley Cain through the Ottawa ICF contract (see above).