Judicial activism refers to the proactive role played by the judiciary in interpreting the Constitution and laws to uphold justice, protect fundamental rights, and sometimes even step into the domains traditionally reserved for the executive and legislature. It often involves judges going beyond strict legal interpretation to address societal needs, fill policy vacuums, or correct perceived executive or legislative inaction or overreach. In India, judicial activism gained prominence, particularly after the Emergency period, largely through Public Interest Litigation (PIL), which allowed any public-spirited individual or organization to approach the courts on behalf of marginalized sections of society.

Its impact on the relationship between the Executive and Judiciary in India is multifaceted:

Positive Impacts:

1. Checks and Balances: Judicial activism acts as a crucial check on executive arbitrariness and legislative inertia, ensuring that the other two pillars of democracy remain accountable and adhere to constitutional principles.
2. Protection of Rights: It has been instrumental in expanding the scope of fundamental rights and ensuring their enforcement, especially for vulnerable groups who might not have had access to justice otherwise.
3. Good Governance: By intervening in matters of public administration, environmental protection, and human rights, the judiciary has often pushed for better governance standards and policy implementation.
4. Filling Policy Gaps: In areas where the executive or legislature has failed to act, the judiciary has sometimes stepped in to provide guidelines or directions, such as in cases of sexual harassment at the workplace (Vishaka guidelines).

Negative Impacts/Challenges:

1. Judicial Overreach: Critics argue that judicial activism can sometimes transform into judicial overreach, where the judiciary encroaches upon the policy-making and executive functions, blurring the lines of separation of powers. This can lead to a perception of the judiciary dictating policy rather than interpreting law.
2. Lack of Expertise: Judges, while experts in law, may not possess the necessary expertise in complex policy matters like economics, defense, or social engineering, leading to potentially impractical or ill-informed directives.
3. Undermining Democracy: Frequent judicial intervention in policy matters can undermine the democratic process by sidelining elected representatives and their accountability to the electorate.
4. Friction between Organs: It often leads to friction and confrontation between the judiciary and the executive/legislature, as seen in debates over appointments, policy decisions, or legislative intent.
5. Accountability Concerns: While the executive and legislature are directly accountable to the public, the judiciary is not, raising questions about accountability when it takes on policy-making roles.

In conclusion, judicial activism in India has been a double-edged sword. While it has played a vital role in upholding justice, protecting rights, and ensuring accountability in a developing democracy, it also presents challenges regarding the delicate balance of power and the principle of separation of powers. A judicious approach, where activism is balanced with judicial restraint, is essential for the healthy functioning of India's democratic institutions.