[R] What does lm() output coefficient mean when it's been given a categorical predictor of string values?

[mviljamaa]

I'm using lm() for a model that has a predictor that has two values 
{poika, tyttö} (boy and girl in Finnish).

I make a model with this categorical variable:

fit1 <- lm(dta$X.U.FEFF..mpist. ~ dta$sukup + dta$HISEI + dta$SES)

and while the variable/vector is here named as dta$sukup, what lm() 
returns is a coefficient

dta$sukuptyttö
      -6.19756

What does the added 'tyttö' in the variable mean? Does it mean that 
'tyttö' has been interpreted as 1 and 'poika' as 0?