It looks to be monitor burn in from a previous program or app.
Image persistence, or image retention, is the LCD and plasma display equivalent of screen burn. Unlike screen burn, however, the effects are usually temporary. Plasma displays can also suffer from burn-in.
Burn-in is permanent damage to a screen caused by showing the same image for a long period of time. ... Burn-in is most prominent in CRT and plasma screens, which use phosphors to create the image on your TV or monitor. However, it's also possible to cause image persistence on an LCD-based screen