"Semi" has two meanings which are used somewhat loosely, which makes things confusing. Something "biweekly" is every other week. Something "semiannually" is twice a year. But "semi" can also mean "somewhat" and is also used as a playful "pseudo", as in "semi-hot". Generally the latter is spelled "semi-" but there's not much consistency. My (U.S.) interpretation of "semi-weekly" is "about once a week - we'll shoot for weekly but no promises".