Object tracking using OpenCV ..I am not able to understand some part of code

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Hello, I am completely new to OpenCV, I am also a bit afraid of asking so basic questions ..I hope I would be helped......Questions: a). Didn't understood this part of code..

# Bitwise-AND mask and original image
res = cv2.bitwise_and(frame,frame, mask= mask)

k = cv2.waitKey(5) & 0xFF
if k == 27:
    break

import cv2
import numpy as np

cap = cv2.VideoCapture(0)

while(1):

    # Take each frame
    _, frame = cap.read()

    # Convert BGR to HSV
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

    # define range of blue color in HSV
    lower_blue = np.array([110,50,50])
    upper_blue = np.array([130,255,255])

    # Threshold the HSV image to get only blue colors
    mask = cv2.inRange(hsv, lower_blue, upper_blue)

    # Bitwise-AND mask and original image
    res = cv2.bitwise_and(frame,frame, mask= mask)

    cv2.imshow('frame',frame)
    cv2.imshow('mask',mask)
    cv2.imshow('res',res)
    k = cv2.waitKey(5) & 0xFF
    if k == 27:
        break

cv2.destroyAllWindows()