The english definition suggests that:
To strum is to play a guitar or another stringed instrument by brushing the strings with your fingers. It's pretty easy to strum a ukulele, but it sounds better if you know some chords.
You might tell the guitar player in your band, "Strum a few chords of that song we wrote yesterday." You can also strum idly on your sister's banjo without playing actual chords, just by running your thumb down the strings. Strum is a noun, too, meaning "the sound or act of strumming." This word dates from the 18th century, and experts think it's imitative, sounding a bit like an actual strum. (Vocabulary.com)
All dictionaries suggest “strimpellare” as a literal translation of the term which, unlike the English term, conveys a more “derogatory” connotation. According to the above definition to “strum” can be used both ways, but it certainly conveys a more neutral connotation.
My take is that there is no perfect literal translation, as suggested also in the following extract:
VERSIONE RITMICA "STRUMMING":
- Serve a scandire il ritmo e la velocità del canto, e valorizza al massimo le armonie. Si suona eseguendo accordi completi, parziali e a singole note accompagnando il canto. È tipica dei "Chitarristi da Spiaggia". Immaginando ogni corda come una voce che canta, è come se suonasse un coro di voci.
Vantaggi: si sente in maniera estremamente chiara sia la ritmica che le armonie.
Svantaggi: dal punto di vista armonico, la modalità "strumming" è approssimata.
Chitarrista di riferimento: Luciano Ligabue.
Esempio di video: "Cosa vuoi che sia" http://www.youtube.com/watch?v=tc_zAS4sFUk