low lying placenta

Just did my 20 wks scan.. sonographer said everything is ok. Cervical length is also good. but in report i saw conclusion: low lying placenta. What is this and is this common at 20 wks? Just curious.. i still have few more days till my gynae appointment and will definitely ask her regarding this. Just wanna knw if any of you face this. To add on, my journey to work is really far. I probably need to walk abt 40 mins one way. Will this affect my pregnancy? Thanks.